1. Field of the Invention
The present invention relates to an electrical filter, and more specifically relates to an electrical filter employing a transverse electromagnetic mode coaxial resonator of a 1/4 wave length in a microwave.
2. Description of the Prior Art
As an electrical filter for use in VHF and UHF band ranges, filters utilizing an LC resonator, coaxial resonator, or the like have been conventionally utilized. However, the filters of the above described types have disadvantages that, in the former type, sufficient selectivity cannot be attained, while in the latter type the size is likely to be large.
Recently, in the field of communication equipment, compactness and light weight of the system are strongly demanded and attempts have been made to reduce the size and weight of various components. However, the fact that it is difficult to make the filter compact and light in weight has retarded the miniaturization and reduction in weight of the system, and in spite of the extensive use of the system due to its importance. Thus, achievement of compact size and light weight of the filters has been mandatory goal for engineers in this field to attain.
On the other hand, filters of excellent selectivity characteristics are desired, depending on the application thereof. However, an attempt to make narrow the bandpass width for the purpose of improving the selectivity characteristic makes the filters less stable with respect to temperature variation and, at the same time, is liable to increase the insertion loss. On the other hand, an attempt to increase the quality factor Q for the purpose of decreasing the insertion loss makes the filter large size and more responsive to spurious noise, etc.